Field of the Invention
The present invention relates to a method for automatically controlling the position of a burden suspended from a main wire of a crane where the burden is connected to at least two tag lines which respectively are connected to the number of the tag lines corresponding winches in which the control of the position of burden is carried out by actuators in the respective winch performing firing/tightening of the respective tag lines, from the signals from the measuring devices placed on the burden and/or the crane, and/or outside of the burden and/or the crane, which is fed to a central monitoring and control unit emitting control signals to the actuators.
Description of Related Art
International Patent Application Publication WO 2011 088832 A1 (AH IND. PROJECTS APS) 28. July 2011 and corresponding U.S. Pat. No. 9,238,569, disclose a method for automatic control of the position of a burden (“load”) suspended in the main wire of a crane, where the burden is connected to at least two tag lines which are connected to a number of winches corresponding to the number of tag lines, where the control of the position of the burden is performed by actuators on the respective winches which performs ease off, tightening of the respective tag lines based on signals from measurement units (tension sensor means) arranged outside the burden, where the signals are processed in a central monitoring- and control unit which transmits control signals to the actuators for the tag lines.
Controlling the position of a burden which is raised above ground level to be mounted in a precise position by means of a main wire of a crane and winches, causes often problems as the burden is exposed to external physical impacts such as wind, and sometimes influences from seas on the crane.
One example of this is the installation of the blades on wind turbines on land and at sea, where wind action on the blade can be a very disturbing element as the blades typically include a mounting flange, whose holes must be brought to overlap a mounting flange on the turbine hub.
The control has so far been carried out by establishing tag lines, so-called “tag lines” extending between the crane, the crane outrigger arm, the burden and secondary winches, which is controlled manually by the crane operator/operators, with a view to control and maintain the burden in a desired position in which it for example, is to be mounted or attached in some other way. This manually performed the control of the secondary winches is in many cases fully sufficient in most assembly work of this kind, but in some occasions, it has nevertheless shown itself to be insufficient, since the compensation of the length of one or more of the tag lines is only carried out, when the crane operator visually may find that the burden has shifted away from the preferred position, which means that a new positioning of the burden to the mounting position is required, with consequent time consumption. The reason that it will not be possible for the operator to compensate the position of the burden, is that the tag lines give way elastically, during the considerable tensile forces are exposed to, which requires a compensatory adjustment of the length of one or more of the tag lines to maintain the burden in a desired mounting position. Taking in consideration, that the hourly rental rate for the cranes is very high, there will be significant savings by being able to avoid the impact of the burden, resulting in the aforementioned positioning of this should be repeated. Further there is a safety issue in preventing the burden from moving, as personnel are present at assembly points for the burden, where sudden shifts of the burden may cause that dangerous work situations with major security risks occur.
In particular, when mounting the blades on large wind turbines on land the above problems occurs, but significantly more pronounced when installing the blades of wind turbines located in territorial waters, where wind impact of the burden/wings are significantly more pronounced and greater than land-based wind turbines but where the wave activity also influences the position of the crane.
The method according to the invention is in particular developed with the intention of being able to control a blade for a wind turbine during installation thereof, but since the method of the invention is applicable generally to the management of a burden suspended from a lifting wire of a crane, there is instead used term “burden” of the item suspended in the main wire of the crane.
Thus, there is a need to be able to perform a better and more efficient management of the position and rotation of a burden suspended in the main wire of a crane, to carry out assembly work on the installation site for the burden safely and quickly, and also in conditions of larger and more external and uncontrollable physical effects of the burden and the crane.